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Old 12-14-2021, 06:47 PM   #1
DCB
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Black Tank Flush — Water Drains From BTF Inlet

I have a built in black tank flush (BTF), and I believe it works properly. However, when I disconnect the hose from the BTF inlet, there is always a substantial amount of water that runs out of the inlet into the convenience center and onto the ground — or onto me, if I don’t get out of the way. Is this normal? I haven’t found any other comments referring to this.

After researching, this is my guess — the water is what was in the line up to the back flow preventer under the bathroom sink. I guess there’s nowhere else for it to go but to run back out of the line.

Am I on the right track? Anything to worry about on this specific issue? (I have read other threads about eliminating/replacing the back flow preventer, and I will probably do that at some point.)

Thanks in advance.
 
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Old 12-14-2021, 07:02 PM   #2
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It's normal. Remove your hose at the water source/spiget. It'll still back flow but not right at face level.
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Old 12-14-2021, 07:18 PM   #3
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Quote:
Originally Posted by jimcol View Post
It's normal. Remove your hose at the water source/spiget. It'll still back flow but not right at face level.
Thanks for the quick response!
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Old 12-14-2021, 08:27 PM   #4
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The black tank flush line has a high point that is 3’-4’ above the level of the black tank. That is where the anti siphon valve is located. Water on the black tank side will drain into the black tank. Water on the inlet side will drain back to the inlet if it does not have a check valve. My older model had a check valve so the water remained in the line.

I never disconnected my flush line until we were moving to a new site.
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Old 12-15-2021, 07:23 AM   #5
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It's a good practice to drain lines such that the convenience center stays dry.
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Old 12-15-2021, 08:44 AM   #6
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Actually, the flush line from the black tank isn't routed uphill from the tank as they just toss it in the bottom of the frame...so it remains full of liquid black tank contents for the first 10 feet or so. Yes, it does eventually go uphill and to it's high point under the bathroom sink or in the shower wall. When I replaced my black tank rinse fitting, I found out how much sewer juices were in that line. I removed the brass close nipple that screws into the plastic rinse fitting and put a check valve in its place.
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Old 12-23-2021, 10:51 AM   #7
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Quote:
Originally Posted by jcurtis934 View Post
Actually, the flush line from the black tank isn't routed uphill from the tank as they just toss it in the bottom of the frame...so it remains full of liquid black tank contents for the first 10 feet or so. Yes, it does eventually go uphill and to it's high point under the bathroom sink or in the shower wall. When I replaced my black tank rinse fitting, I found out how much sewer juices were in that line. I removed the brass close nipple that screws into the plastic rinse fitting and put a check valve in its place.
If you put a check valve in the line, how do you winterize that section?
Thanks Rick
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Old 12-23-2021, 01:41 PM   #8
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Personally I don’t use the BTF on any RV I’ve ever owned.. the anti siphon valve (OEM) is junk and will crack and leak.. the little sprayer at the end inside the tank is a joke at best…

I prefer to use the Valtera King flush .. I can clean not only the black tank but they gray tanks as well..and yes, the gray tank the kitchen sink drains into always has left over food particles ..using the king flush I get the tanks clean

It’s also nice with that external gate valve and clear section.. I don’t get unwanted messes when I remove the sewer cap due to a holding tank valve that didn’t fully seat..and they will all do this from time to time

I can’t even begin to count the number of 8mages and posts I’ve seen over the years where folks have flooded their RV due to a cracked anti siphon valve..

If you are gonna use it then upgrade the valve to a brass one..

Image’s of typical OEM black tank sprayer..
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Old 12-23-2021, 01:59 PM   #9
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Here's a photo of my convenience center:



If you notice, I attached a green (short) garden hose to the black tank flusher and I just leave it there permanently. So, when I run my black tank flusher, I can just connect the hose to the green one already there.

Why? First, connecting hoses to the inlet on the camper is very hard, because of it's location. Second, when connecting at the inlet, it often leaks. It's hard to get it tight so water does not spray everywhere. Third, the inlet on the camper is a soft plastic, and easy to cross thread or damage with repeated screwing on and off wearing down the threads.

By attaching another hose, it saves the threads on the trailer connection, and then when I disconnect, the water that back feeds under pressure can be drained outside the convenience center by simply lowering the hose. I keep it there permanently. It's never been taken off since I put it on there.

Also, this is a very, very easy way to run the black tank rinser when there is no shore water available. Simply connect that blue hose for the shower to the garden hose, and turn on the shower. This works very well, as almost always, the hose provided at dump stations is way to short to reach the front end of the camper and the black tank outlet as at the end of this 41 foot behemoth.

It's an easy solution .... IF you can find a short garden hose. I think the one in the photo is 5 feet.
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Old 01-02-2022, 07:06 AM   #10
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Backflush

When you use the Valterra backslash king how do you know when you have enough water in the tank so you don't overfill and is there a concern for the back pressure it creates.
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Old 01-02-2022, 08:08 AM   #11
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I have aa inline flow meter on my Black Tank Flush and one for my Fresh Water Fill. Lets me know exactly how much water goes in.
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Old 01-02-2022, 09:28 AM   #12
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I use the clear plastic Valterra flush elbow fitting so I can see when cleanish water is coming out of the tanks. From time to time I hook a water hose up to it for a backflush. At some point - the weight of the water that has “filled” the tank overcomes the pressurized water coming from the hose. I can see more water coming out/draining than the hose can keep up with. That is the point where I turn off the hose and let the tank completely drain. I can’t prove it but I don’t think the hose bibs at my house or at the the RV parks have enough volume or pressure to fill the tanks to overfill. Gravity seems to always win.
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